It is well-known that the familiar incandescent lamp functions primarily as a resistor in an electric circuit. Light is produced because of the high temperature to which the filament is heated by power losses which vary in proportion to both the first power of filament resistance and the square of the filament current. The filament resistance is essentially a constant except for comparatively small changes which are caused by variations in filament temperature. The lamp can be energized quite safely by direct connection to any electric power source of appropriate voltage.
It is also well-known that a discharge type lamp, whether it employs a fluorescent coating or not, is not so simple in its operation. Its resistance is many megohms when it is in the passive state, and its operation depends upon the establishment of an arc through an internal cloud of ions called a plasma, the arc being initiated by an application of high voltage or by other well-known means.
After the arc has been established, the electrical behavior of the lamp is complex. If the applied voltage decreases below a critical value, the arc will be extinguished and the resistance of the lamp will revert to the multi-megohm range.
On the other hand, the resistance of the arc varies during lamp operation in a way such that the lamp current is not stable when the applied voltage is held at a constant value. Immediately after being struck, the arc resistance decreases and the lamp current rises to destructive values unless preventive measures have been employed.
The above-described behavior of arcs in the plasmas of discharge-type lamps has often been prevented by the insertion of an impedance (either resistive, inductive, capacitive, or some combination thereof) in series with the lamp and its power supply. This solution to the problem of destructive overcurrent has been employed so often that it is often erroneously believed that a series impedance is a fundamental necessity for a discharge-type lamp.
It is occasionally claimed that some means for maintaining a literally uninterrupted current through a discharge-type lamp is necessary to prevent the arc from being extinguished.
A more accurate description of arc behavior is taught herein, and experimental evidence to verify that description is presented. A unique ballast, based on the resulting comprehension of lamp characteristics, is then described.